It would be more of a personal preference type thing. 1950 DeLuxes used a cut pile carpet with a rubber backing while the Specials used a loop. Below is a detail photo of the cut pile from a 1951 DeLuxe.
1951 Fleetline Preservation
'51 Fleetline DeLuxe 2 DOOR SEDAN (Fathom Green)
'51 Styleline Special BUSINESS COUPE (Shadow Gray)
'53 6500 Dump Bed (Oxidized Red)
'50 Styleline DeLuxe 4 DOOR SEDAN (Mist Green)
Ken Sluys pointed out to me that sometime mid year 1950 the Belair changed from the rubber mat and offered carpeting in the front.
1951 Fleetline Preservation
'51 Fleetline DeLuxe 2 DOOR SEDAN (Fathom Green)
'51 Styleline Special BUSINESS COUPE (Shadow Gray)
'53 6500 Dump Bed (Oxidized Red)
'50 Styleline DeLuxe 4 DOOR SEDAN (Mist Green)